Diamond enhanced buttons (DE-buttons) for percussive drilling and rotary drilling usually have semispherical, ballistical, conical or chisel shaped tips. The outer hard polycrystalline diamond layer (PCD-layer) is very thin, normally 0.2 mm and the service length of the button is directly related to how fast the PCD-layer is worn through. To get the most from the DE-buttons the DE-bits normally are designed to distribute the wear as evenly as possible, i.e. the gauge buttons that often are determining the service length are placed symmetrically and also the bit as a whole often has a more or less symmetrical shape, such as shown in Hedlund et al. U.S. Pat. No. 5,575,342. A way to increase the service length would be to increase the thickness of the PCD-layer. However, for technical and physical reasons it has not been possible to make the PCD-layer much thicker than 0.4 mm on semispherical buttons for percussive and rotary drilling.
DE-button bits are most useful when drilling in hard to extra hard abrasive rock where DE-button bits have the advantage that they do not need to be reground, while the wear on conventional cemented carbide-buttons is high, requiring regrinding several times.
U.S. Pat. No. 5,335,738 discloses a button of cemented carbide with a stud covered by a diamond layer. The PCD layer is thicker at certain parts of the button, for example at the tip point where a shallow hole in the substrate is provided and on the flank wherein a shallow groove around the semispherical tip is provided. The known button has a layer which provides less disadvantageous stresses and locally thicker PCD-layer. The service length of the known button has, in spite of these improvements, not been optimized. Dennis U.S. Pat. No. 5,379,854 discloses in one embodiment a button of cemented carbide with a diamond layer. The button surface has a sinusoidal cross section and an applied PCD-layer of similar contour. The ridges and the grooves of the sinusoidal contour of the cemented carbide button serve to prevent delamination of the PCD-layer and reduce the shear stresses in the bond zone between the PCD-layer and the cemented carbide. The sinusoidal profile of the PCD-layer provides several impact points which work simultaneously when the button is used for drilling.